This invention relates to a circuit for use with a telephone pay station for providing coin-free dialing of a preselected number of digits as well as a circuit for the prevention of fraudulent push-button chain-dialing. More particularly, it relates to a circuit for providing a phantom coin signal to a telephone central office for a predetermined number of digits dialed as well as a means for shunting the push-button dial if fraudulent chain-dialing is attempted.
Telephone pay stations using both rotary and push-button dialing are currently in wide use. A coin must be inserted in most pay stations in order to dial any number whether it be one, three, or any number of digits. Some of these numbers, such as one digit (operator) and three digits (information, emergency, or service calls) have been designated as free calls. Once the coin has been inserted and the call made, the central office, either manually or electronically, refunds the coin. This method of operation prevents what may be an emergency call because the potential caller lacks the proper coin. It is therefore desirable to provide a pay station having coin-free service for certain numbers such as information and emergency numbers.
Limited coin-free service has been provided in the past utilizing mechanical relays and mechanically counter to prevent more than a preselected number of digits to be dialed. An example of such a circuit is set forth in U.S. Pat. No. 3,678,203. This relay type circuit, however, is subject to contact wear, coin totalizing limits, mechanical failures, and therefore requires frequent servicing.
Another type of coin-free service is shown in U.S. Pat. No. 3,676,597. This patent shows central office equipment used to decode the dial pulse and provide coin-free service from a normal pay station. The present invention does not require replacement or modificaton of central office equipment but only the addition of a circuit module to a pay station where coin-free dialing is desired.